Magneto-resistive random access memory (MRAM) is a non-volatile random access memory technology that uses magnetic storage elements to store data. MRAM stores data at memory cells having two superimposed layers of magnetic material separated by a thin insulating film, defining a magnetic tunnel junction (“MTJ” or “MTJ element”) of an MRAM cell. The two layers include a magnetic layer that is permanently magnetized in a fixed magnetic field alignment direction (this layer is referred to as a pinned layer), and a changeably-magnetized magnetic layer (this layer is referred to as a free layer). The changeably-magnetized magnetic layer can be magnetized in one of two orientations relative to the permanently magnetized layer. The two orientations are characterized by distinctly different serial resistances through the superimposed layers of the MTJ. The magnetic field orientation of the changeable layer can be aligned the same as that of the permanent magnet layer (parallel), or the magnetic field of the changeable layer can be aligned directly opposite to that of the permanent magnet layer (anti-parallel). The parallel alignment state has a relatively lower resistance and the anti-parallel alignment state has a higher resistance.
The two states of an MRAM cell are sensed from their relatively higher or lower resistances (RH and RL), which represent different binary logic values of a bit stored in the memory. A reference voltage is applied to the MRAM cell, and the resulting cell current can be used to determine whether the cell is in the low resistance state or the high resistance state. For this purpose, a sense amplifier is typically used to compare the cell current against a reference current.